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virtiofsd: jail lo->proc_self_fd

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While it's not possible to escape the proc filesystem through
lo->proc_self_fd, it is possible to escape to the root of the proc
filesystem itself through "../..".

Use a temporary mount for opening lo->proc_self_fd, that has it's root at
/proc/self/fd/, preventing access to the ancestor directories.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Message-Id: <20200429124733.22488-1-mszeredi@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Miklos Szeredi 2020-04-29 14:47:33 +02:00 committed by Dr. David Alan Gilbert
parent 8c1d353d10
commit 397ae982f4
1 changed files with 27 additions and 4 deletions
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31
tools/virtiofsd/passthrough_ll.c
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@ -2536,6 +2536,8 @@ static void print_capabilities(void)
static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
{
pid_t child;
char template[] = "virtiofsd-XXXXXX";
char *tmpdir;
/*
* Create a new pid namespace for *child* processes. We'll have to
@ -2597,12 +2599,33 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
exit(1);
}
/* Now we can get our /proc/self/fd directory file descriptor */
lo->proc_self_fd = open("/proc/self/fd", O_PATH);
if (lo->proc_self_fd == -1) {
fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
tmpdir = mkdtemp(template);
if (!tmpdir) {
fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template);
exit(1);
}
if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) {
fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n",
tmpdir);
exit(1);
}
/* Now we can get our /proc/self/fd directory file descriptor */
lo->proc_self_fd = open(tmpdir, O_PATH);
if (lo->proc_self_fd == -1) {
fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir);
exit(1);
}
if (umount2(tmpdir, MNT_DETACH) < 0) {
fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir);
exit(1);
}
if (rmdir(tmpdir) < 0) {
fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir);
}
}
/*